Backwash strainers are well known in the art. For example, U.S. Pat. No. 4,328,103 to Kraeling, Jr. et al. (the “Kraeling '103 patent”) discloses such a strainer for filtering particulate debris from a liquid. The strainer includes a hollow body which houses a filtering element in the form of a cylindrical screen. A rotatable backwash arm is positioned within the cylindrical screen.
During a filtering operation, liquid with debris flows into the strainer through an inlet. After flowing upwardly into the interior of the cylindrical screen, the debris-laden liquid flows radially outward through openings in the screen. At least some of the debris collects on an inner surface of the screen. The filtered liquid exits the strainer through an outlet.
Over time, the screen becomes clogged with the collected debris, thereby necessitating the performance of a backwash operation to clear the screen. During the performance of such a backwashing operation, the backwash arm is rotated to continuously isolate portions of the screen and, through the creation of a pressure differential, causes a reverse flow of liquid so as to force the collected debris into the backwash arm for discharge from the strainer.
Although backwash strainers such as the one disclosed in the Kraeling '103 patent have been commercially successful, it is always desirable to reduce clogging of the screen, because such clogging has a detrimental affect on the overall efficiency of the strainer. More particularly, as the frequency and duration of clogging increases, the frequency and duration at which the backwash operation must be performed increases, thereby reducing the total volume of liquid filtered by the strainer over time. What is needed therefore is a backwash strainer having means for inhibiting clogging so to maximize strainer efficiency.